Is there a valid domain name guaranteed to be unreachable?

Question

Is there a valid domain name used by convention for test cases where the host is supposed to be unreachable? E.g. http://www.unreachable.net/ or http://www.downforever.net/ which seem to be down right now - but for how long?

Or at least an IP address guaranteed to be unreachable? (The Special-Use IPv4 Address spec https://www.rfc-editor.org/rfc/rfc3330 does not seem to mention such an address).

UPDATE: The top-level domain invalid in https://www.rfc-editor.org/rfc/rfc2606 comes close (thanks JOTN), but I'm looking for a domain that can be resolved to an IP which is not reachable (i.e. no server responds).

Answer 1

What do you mean by valid? There's the reserved top level domain: example, invalid, localhost, and test.

It talks about those here:

http://en.wikipedia.org/wiki/Top-level_domain#Reserved_domains